A motor for use in a small appliance which has an oscillating action will typically include a restoring mechanism, such as a spring of some kind, which in operation provides a selected amount of torque, depending upon the particular application. The design requirements for the oscillating action are determined by the system spring rate required to provide the desired mechanical resonant frequency of the spring mass assembly. The electrical and mechanical operating frequencies, which includes the resonant frequency of the spring mass system, must be balanced in order to optimize performance of the appliance. In many applications, a low profile (low height) of the appliance is important for the user's convenience, which places significant limitations on the overall configuration of the spring mass system.
Various motor structures for small appliances are known, with each system having particular advantages and disadvantages, depending on the application requirements. A torsion tube spring has been used to provide the restoration function of an oscillating motor, but torsion tubes are not readily available in the highest strength spring material and therefore often require a longer length than is feasible for the present embodiment. Clamping the ends of torsion tubes, without collapsing the tubes, presents another significant challenge for a torsion tube embodiment. Non-axial torsion wire arrangements can be used, but such an arrangement results in high stress on the individual wires, as well as excessive Z-axis movement. Another possible approach uses pairs of ribbon or leaf springs, but such an arrangement has a high cost and produces excessive stresses on the spring members. Also, many of these approaches are often too complex for extended reliable operation.
Hence, in a personal care appliance, such as a skin care appliance, which uses an oscillating workpiece, a motor arrangement is desirable which is low profile, reliable in operation, and able to withstand the stresses inherent in oscillating action.